A new study from researchers at the University of California at Santa Barbara sheds light (pun intended) on that very question.
It turns out that despite the fact that octopuses have eyes and brains (which they actually put to good use) — not to mention several hearts — they actually don't need to use those to sense changes in light around them.
Their skin tissue can do that all on their own.
"Octopus skin doesn't sense light in the same amount of detail as the animal does when it uses its eyes and brain," said lead author Desmond Ramirez, a doctoral student in the UCSB Department of Ecology, Evolution and Marine Biology. “But it can sense an increase or change in light. Its skin is not detecting contrast and edge but rather brightness.”
To test this, researchers exposed the octopus skin to different kinds of light. They found that that in response to light, the organ that expands or contracts to change the color of the octopus's skin, or chromatophores, expanded and changed color. They call the process Light-Activated Chromatophore Expansion or LACE.
In octopuses' skin tissue, researchers found a protein that is usually found in its eye, leading them to believe that the animals have evolved to use the same mechanism for light detection in both places.
“It looks like the existing cellular mechanism for light detection in octopus eyes, which has been around for quite some time, has been co-opted for light sensing in the animal’s skin and used for LACE,” explained co-author and UCSB professor Todd Oakley. “So instead of completely inventing new things, LACE puts parts together in new ways and combinations.”
Octopuses aren't the only mollusks that do this sort of thing. But these findings do help to piece together more about the octopuses evolutionary relatives.
And the animals' unique skill at camouflage is something that could potentially have big implications for us humans, who are, of course, trying to figure out how to make synthetic materials that mimic the octopuses' signature talent.